Transepithelial Fluid and Salt Re-Absorption Regulated by cGK2 Signals

Network pharmacology-based research into the mechanism of ferulic acid on acute lung injury through enhancing transepithelial sodium transport

ETHNOPHARMACOLOGICAL RELEVANCE

Ferulic acid (FA) has shown potential therapeutic applications in treating lung diseases. However, the underlying mechanisms by which FA ameliorates acute lung injury (ALI) have not been distinctly elucidated.

AIM OF THE STUDY

The project aims to observe the therapeutic effects of FA on lipopolysaccharide-induced ALI and to elucidate its specific mechanisms in regulating epithelial sodium channel (ENaC), which majors in alveolar fluid clearance during ALI.

MATERIALS AND METHODS

In this study, the possible pathways of FA were determined through network pharmacology analyses. The mechanisms of FA in ALI were verified by in vivo mouse model and in vitro studies, including primary alveolar epithelial type 2 cells and three-dimensional alveolar organoid models.

RESULTS

FA ameliorated ALI by improving lung pathological changes, reducing pulmonary edema, and upregulating the α/γ-ENaC expression in C57BL/J male mice. Simultaneously, FA was observed to augment ENaC levels in both three-dimensional alveolar organoid and alveolar epithelial type 2 cells models. Network pharmacology techniques and experimental data from inhibition or knockdown of IkappaB kinase β (IKKβ) proved that FA reduced the phosphorylation of IKKβ/nuclear factor-kappaB (NF-κB) and eliminated the lipopolysaccharide-inhibited expression of ENaC, which could be regulated by nuclear protein NF-κB p65 directly.

CONCLUSIONS

FA could enhance the expression of ENaC at least in part by inhibiting the IKKβ/NF-κB signaling pathway, which may potentially pave the way for promising treatment of ALI.

Analysis of abnormal expression of signaling pathways in PQ-induced acute lung injury in SD rats based on RNA-seq technology

Background: Paraquat (PQ) plays an important role in agricultural production due to its highly effective herbicidal effect. However, it has led to multiple organ failure in those who have been poisoned, with damage most notable in the lungs and ultimately leading to death. Because of little research has been performed at the genetic level, and therefore, the specific genetic changes caused by PQ exposure are unclear.Methods: Paraquat poisoning model was constructed in Sprague Dawley (SD) rats, and SD rats were randomly divided into Control group, paraquat (PQ) poisoning group and Anthrahydroquinone-2,6-disulfonate (AH2QDS) treatment group. Then, the data was screened and quality controlled, compared with reference genes, optimized gene structure, enriched at the gene expression level, and finally, signal pathways with significantly different gene enrichment were screened.Results: This review reports on lung tissues from paraquat-intoxicated Sprague Dawley (SD) rats that were subjected to RNA-seq, the differentially expressed genes were mainly enriched in PI3K-AKT, cGMP-PKG, MAPK, Focal adhesion and other signaling pathways.Conclusion: The signaling pathways enriched with these differentially expressed genes are summarized, and the important mechanisms mediated through these pathways in acute lung injury during paraquat poisoning are outlined to identify important targets for AH2QDS treatment of acute lung injury due to paraquat exposure, information that will be used to support a subsequent in-depth study on the mechanism of PQ action.

Avanafil as a Novel Therapeutic Agent Against LPS-Induced Acute Lung Injury via Increasing CGMP to Downregulate the TLR4-NF-κB-NLRP3 Inflammasome Signaling Pathway

AIM

We demonstrate the effect of PDE5 inhibitors in cases of acute lung injury via the relationship between cGMP/NO and the TLR4-NF-κB-NLRP3 pathway.

MATERIALS AND METHODS

This study was performed with 30 male Wistar albino rats. Lipopolysaccharide (LPS) was administered intratracheally to the rats and acute lung injury (ALI) was induced. Twelve hours after LPS administration, avanafil, prepared at suitable doses according to the body weights of the animals, was administered by oral gavage. Lung tissue samples of all groups were examined histopathologically and by immunochemical staining (IL-1β, iNOS, TLR4, and NF-κB). The iNOS, NLRP3, and IL-1B mRNA expression levels in the lung tissues were measured by RT-PCR. The left upper lobes of the rat lungs were dried at 70 °C for 48 h and lung water content was calculated.

RESULT

Statistically significant increases in iNOS, NLRP3, and IL-1β mRNA expressions were observed in the rats with ALI compared to the healthy controls (p < 0.0001). Those increased expressions were reduced at both doses of avanafil (p < 0.0001). This reduction was found to be greater at 20 mg/kg (p < 0.0001). IL-1β, iNOS, TLR4, and NF-κB immunopositivity was moderate/severe in the ALI group and mild in the group with ALI + avanafil at 20 mg/kg (p < 0.05). When the wet/dry lung ratios were calculated, a statistically significant increase was seen in the ALI group compared to the healthy rats (p < 0.05). That increase was decreased with both avanafil doses (p < 0.05).

CONCLUSION

We suggest that avanafil may prevent the progression of ALI and be effective in its treatment. We hope that this study will be supported by future clinical studies to yield a new indication for avanafil.

Prkg2 regulates alveolar type 2-mediated re-alveolarization

BACKGROUND

The cGMP-dependent type 2 protein kinase, encoded by the prkg2 gene, is highly expressed in alveolar type 2 epithelial (AT2) cells. It is unclear whether prkg2 regulates AT2 cell homeostasis and re-alveolarization of injured lungs. This study aimed to investigate the role of prkg2 in the regulation of the fate of AT2 in vitro.

METHODS

Primary AT2 cells of wild-type (wt) and prkg2^-/- mice were co-cultured with fibroblasts as three-dimensional organoids. The colony formation was analyzed between days 4 and 12 post-seeding. EdU assay was used to detect cells with active DNA synthesis. AT1 and AT2 cells in organoids were visualized with anti-podoplanin and anti-surfactant protein C antibodies, respectively.

RESULTS

Prkg2^-/- AT2 cells developed a greater number of organoids than wt controls. However, compared to wt organoids, a lower number of AT2 but a greater number of AT1 cells were visualized. In addition, a lower number of proliferated cells (EdU⁺) were observed in prkg2^-/- organoids compared to wt controls. The numbers of organoids and EdU⁺ cells were significantly reduced in protein kinase A (PKA) inhibitor H89-treated wt and prkg2^-/- cultures. Organoids and EdU⁺ cells were increased by lipopolysaccharides (LPS) in both wt and prkg2^-/- groups. The increase in the proportion of AT1 and AT2 cells in organoids was only seen in wt controls.

CONCLUSIONS

Prkg2 may regulate the lineage of AT2 cells, which is affected by endotoxins and the interactive PKA signaling pathway.

Luteolin attenuates lipopolysaccharide-induced acute lung injury/acute respiratory distress syndrome by activating alveolar epithelial sodium channels via cGMP/PI3K pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Luteolin (Lut) was recently identified as the major active ingredient of Mosla scabra, which was a typical representative traditional Chinese medicine and had been used to treat pulmonary diseases for thousands of years.

AIM OF THE STUDY

This study was to explore the effects and relative mechanisms of Lut in LPS-induced acute lung injury/acute respiratory distress syndrome (ALI/ARDS). The main characteristic of ALI/ARDS is pulmonary edema, and epithelial sodium channel (ENaC) is a key factor in effective removal of excessive alveolar edematous fluid, which is essential for repairing gas exchange and minimizing damage to the peripheral tissues. However, whether the therapeutic effects of Lut on respiratory diseases are relative with ENaC is still unknown.

MATERIALS AND METHODS

Alveolar fluid clearance was calculated in BALB/c mice and ENaC function was measured in H441 cells. Moreover, ENaC membrane protein and mRNA were detected by Western blot and real-time PCR, respectively. We also studied the involvement of cGMP/PI3K pathway during the regulation of Lut on ENaC during LPS-induced ALI/ARDS by ELISA method and applying cGMP/PI3K inhibitors/siRNA.

RESULTS

The beneficial effects of Lut in ALI/ARDS were evidenced by the alleviation of pulmonary edema, and enhancement of both amiloride-sensitive alveolar fluid clearance and short-circuit currents. Lut could alleviate the LPS decreased expression levels of ENaC mRNA and membrane protein in H441 cells and mouse lung. In addition, cGMP concentration was increased after the administration of Lut in ALI/ARDS mice, while the inhibition of cGMP/PI3K pathway could abrogate the enhanced AFC and ENaC protein expression of Lut.

CONCLUSION

These results implied that Lut could attenuate pulmonary edema via enhancing the abundance of membrane ENaC at least partially through the cGMP/PI3K pathway, which could provide a promising therapeutic strategy for treating ALI/ARDS.

Extracellular protein kinase A and G are potential biomarkers of some inflammation-associated disorders

Introduction

Protein kinase A (PKA) and protein kinase G (PKG) are the main downstream effectors of second messengers cAMP and cGMP, which play important roles in physiological and pathological processes. Recently, there are two findings: one is PKA catalytic subunits α (PKACα) and PKG II can be secreted, the other is that the two secretory protein kinases are associated with the progression of tumors. Previous data also demonstrate that the two kinases, as signal cascades, involved in inflammation-associated disorders. However, it remains unclear whether the secreted PKACα or PKG II could serve as diagnostic biomarkers for inflammation-associated disorders.

Methods

The serum from suffered coronary disease, diabetes, rheumatoid arthritis, and schizophrenia were collected. The serum PKACα and PKG II were detected by ELISA. All the patients were consent informed.

Results

Our results showed that the serum PKACα and PKG II had obvious changes in coronary disease, rheumatoid arthritis, schizophrenia patients. However, the trends was opposite, especially in rheumatoid arthritis.

Conclusions

Serum PKACα and PKG II could serve as potentially diagnostic biomarkers for some inflammation-associated disorders, such as coronary disease, rheumatoid arthritis, and schizophrenia.

Conditioned Medium of Bone Marrow Mesenchymal Stem Cells Involved in Acute Lung Injury by Regulating Epithelial Sodium Channels via miR-34c

Background

One of the characteristics of acute lung injury (ALI) is severe pulmonary edema, which is closely related to alveolar fluid clearance (AFC). Mesenchymal stem cells (MSCs) secrete a wide range of cytokines, growth factors, and microRNA (miRNAs) through paracrine action to participate in the mechanism of pulmonary inflammatory response, which increase the clearance of edema fluid and promote the repair process of ALI. The epithelial sodium channel (ENaC) is the rate-limiting step in the sodium–water transport and edema clearance in the alveolar cavity; the role of bone marrow-derived MSC-conditioned medium (BMSC-CM) in edema clearance and how miRNAs affect ENaC are still seldom known.

Methods

CCK-8 cell proliferation assay was used to detect the effect of BMSC-CM on the survival of alveolar type 2 epithelial (AT2) cells. Real-time polymerase chain reaction (RT-PCR) and western blot were used to detect the expression of ENaC in AT2 cells. The effects of miR-34c on lung fluid absorption were observed in LPS-treated mice in vivo, and the transepithelial short-circuit currents in the monolayer of H441 cells were examined by the Ussing chamber setup. Dual luciferase reporter gene assay was used to detect the target gene of miR-34c.

Results

BMSC-CM could increase the viability of mouse AT2 cells. RT-PCR and western blot results showed that BMSC-CM significantly increased the expression of the γ-ENaC subunit in mouse AT2 cells. MiR-34c could restore the AFC and lung wet/dry weight ratio in the ALI animal model, and Ussing chamber assay revealed that miR-34c enhanced the amiloride-sensitive currents associated with ENaC activity in intact H441 cell monolayers. In addition, we observed a higher expression of miR-34c in mouse AT2 cells administrated with BMSC-CM, and the overexpression or inhibition of miR-34c could regulate the expression of ENaC protein and alter the function of ENaC. Finally, we detected that myristoylated alanine-rich C kinase substrate (MARCKS) may be one of the target genes of miR-34c.

Conclusion

Our results indicate that BMSC-CM may alleviate LPS-induced ALI through miR-34c targeting MARCKS and regulate ENaC indirectly, which further explores the benefit of paracrine effects of bone marrow-derived MSCs on edematous ALI.

Phylogenic Determinants of Cardiovascular Frailty, Focus on Hemodynamics and Arterial Smooth Muscle Cells

The evolution of the circulatory system from invertebrates to mammals has involved the passage from an open system to a closed in-parallel system via a closed in-series system, accompanying the increasing complexity and efficiency of life’s biological functions. The archaic heart enables pulsatile motion waves of hemolymph in invertebrates, and the in-series circulation in fish occurs with only an endothelium, whereas mural smooth muscle cells appear later. The present review focuses on evolution of the circulatory system. In particular, we address how and why this evolution took place from a closed, flowing, longitudinal conductance at low pressure to a flowing, highly pressurized and bifurcating arterial compartment. However, although arterial pressure was the latest acquired hemodynamic variable, the general teleonomy of the evolution of species is the differentiation of individual organ function, supported by specific fueling allowing and favoring partial metabolic autonomy. This was achieved via the establishment of an active contractile tone in resistance arteries, which permitted the regulation of blood supply to specific organ activities via its localized function-dependent inhibition (active vasodilation). The global resistance to viscous blood flow is the peripheral increase in frictional forces caused by the tonic change in arterial and arteriolar radius, which backscatter as systemic arterial blood pressure. Consequently, the arterial pressure gradient from circulating blood to the adventitial interstitium generates the unidirectional outward radial advective conductance of plasma solutes across the wall of conductance arteries. This hemodynamic evolution was accompanied by important changes in arterial wall structure, supported by smooth muscle cell functional plasticity, including contractility, matrix synthesis and proliferation, endocytosis and phagocytosis, etc. These adaptive phenotypic shifts are due to epigenetic regulation, mainly related to mechanotransduction. These paradigms actively participate in cardio-arterial pathologies such as atheroma, valve disease, heart failure, aneurysms, hypertension, and physiological aging.

Ion transport mechanisms for smoke inhalation-injured airway epithelial barrier

Smoke inhalation injury is the leading cause of death in firefighters and victims. Inhaled hot air and toxic smoke are the predominant hazards to the respiratory epithelium. We aimed to analyze the effects of thermal stress and smoke aldehyde on the permeability of the airway epithelial barrier. Transepithelial resistance (R_TE) and short-circuit current (I_SC) of mouse tracheal epithelial monolayers were digitized by an Ussing chamber setup. Zonula occludens-1 tight junctions were visualized under confocal microscopy. A cell viability test and fluorescein isothiocyanate-dextran assay were performed. Thermal stress (40 °C) decreased R_TE in a two-phase manner. Meanwhile, thermal stress increased I_SC followed by its decline. Na⁺ depletion, amiloride (an inhibitor for epithelial Na⁺ channels [ENaCs]), ouabain (a blocker for Na⁺/K⁺-ATPase), and CFTRinh-172 (a blocker of cystic fibrosis transmembrane regulator [CFTR]) altered the responses of R_TE and I_SC to thermal stress. Steady-state 40 °C increased activity of ENaCs, Na⁺/K⁺-ATPase, and CFTR. Acrolein, one of the main oxidative unsaturated aldehydes in fire smoke, eliminated R_TE and I_SC. Na⁺ depletion, amiloride, ouabain, and CFTRinh-172 suppressed acrolein-sensitive I_SC, but showed activating effects on acrolein-sensitive R_TE. Thermal stress or acrolein disrupted zonula occludens-1 tight junctions, increased fluorescein isothiocyanate-dextran permeability but did not cause cell death or detachment. The synergistic effects of thermal stress and acrolein exacerbated the damage to monolayers. In conclusion, the paracellular pathway mediated by the tight junctions and the transcellular pathway mediated by active and passive ion transport pathways contribute to impairment of the airway epithelial barrier caused by thermal stress and acrolein. Graphical abstract Thermal stress and acrolein are two essential determinants for smoke inhalation injury, impairing airway epithelial barrier. Transcellular ion transport pathways via the ENaC, CFTR, and Na/K-ATPase are interrupted by both thermal stress and acrolein, one of the most potent smoke toxins. Heat and acrolein damage the integrity of the airway epithelium through suppressing and relocating the tight junctions.

Regulation of Cl- Electrolyte Permeability in Epithelia by Active Traditional Chinese Medicine Monomers for Diarrhea

The epithelial layer, lining the inner surface of the mammalian alveolar, kidney, brain and colon, is a typical electrolyte transporting tissue. Large quantities of salt and fluid are actively moved from the mucosal side toward the blood vessel. Transepithelial salt re-absorption in epithelial tissues plays an important role in maintaining fluid homeostasis. In absorptive epithelium, fluid and salt flux is controlled by the machinery mainly composed of epithelial sodium channel, cystic fibrosis transmembrane conductance regulator, Na+-K+-2Cl- cotransporter, Na+/H+ exchanger, and Na+/K+-ATPase. Dysregulation of salt permeability across epithelium contributes to the pathogenesis of organ edema. In numerous ion transporters, epithelial Cl- transportation plays an important role in water secretion across epithelial tissues and regulation of body fluid content. Many traditional Chinese medicines treat diarrhea by regulating the Cl- electrolyte transport. We systematically summarized the recent progress regarding the traditional Chinese medicine on Cl- electrolyte transport in the intestinal epithelial tissues. The pharmaceutical relevance of developing advanced strategies to mitigate edematous disorders is also implicated. In conclusion, the crosstalk between Cl- electrolyte transport and active traditional Chinese medicine monomers may lead to the development of new strategies for diarrhea by manipulating the function and expression of ion channels.